Method of electroslag welding of light metals, forming device and flux

ABSTRACT

A method of electroslag welding of light metals wherein parts to be welded, a forming device, and an electrode are successively mounted with the provision of a required gap between said parts, following which the gap is filled with a flux, and then a slag pool is set up with following melting of the electrode and the edges with the formation of a metal pool, which is accumulated, maintained in the liquid state and utilized for filling the welding gap with the liquid metal with subsequent solidification of the liquid metal. According to the invention, the metal pool is accumulated outside the gap above the parts being welding, and filling the gap with the liquid metal is carried out after the termination of fusion of the electrode and the parts being welded and accumulation of the metal pool in a volume required for filling the gap considering weld reinforcement. 
     The method is carried out by means of a forming device which comprises moulds (9), a container (13) disposed above the parts to be welded, and a container (14) disposed under the parts to be welded. According to the invention, the moulds (9) are further provided with porous elements (12) and are constructed with stepped porous grooves (10) forming a supporting platform (11) on which are disposed said porous elements (12) forming with the grooves (10) enclosed cavities. The container (13) disposed above the parts to be welded is further provided with external (16) and internal (17) terminals and a jumper (18) connecting the internal terminals (17). The container (14) disposed under the parts to be welded is further provided with a transverse partition (27). 
     The flux utilized in the welding process comprises cryolite, barium fluoride and alkali metal bromide.

TECHNICAL FIELD

The invention relates to welding production, and particularly toelectroslag welding of light metals whose density is lower than that ofa flux, to a forming device for practicing said method, and to a fluxutilized in this process.

BACKGROUND ART

Known in the art is a method of electroslag welding of light metals,consisting in successively mounting parts to be welded, with a desiredgap therebetween, a forming device, and an electrode (USSR Inventor'sCertificate No. 764,902). Following this, the gap between the edges tobe welded is filled with a flux, leaving the electrode end extended overthe flux surface, and a slag pool is set up. Then the welding current isswitched on. As the volume of the slag pool increases, the bottomportion thereof is lowered while exposing new portions of the electrodefor melting. In the process of welding the electrode is melted fromabove downwards, while liquid metal formed as a result of melting theelectrode and the slag pool are kept within the gap. After the completemelting of the electrode and fusion of the edges of the parts to bewelded, the welding current is disconnected. Metal is solidified withinthe gap thereby forming a weld.

A device for practicing this method comprises side moulds, a containerdisposed above the edges to be welded, and a container disposed undersaid edges. The upper container is defined by the side moulds and barsmounted on the parts to be welded. The lower container in defined by theside moulds and bars mounted under the parts to be welded. The lowercontainer further comprises a tray retaining the flux and the weld poolwithin the gap.

The weld obtained by the prior art method with the use of the abovedevice possesses insufficiently high performance properties due toincomplete degassing of the weld metal. In the utilization of the abovedevice the setting of the slag pool is also impeded.

Known in the art is a halide-based flux (U.S. Pat. No. 3,585,343),containing in percent by weight:

    ______________________________________                                        potassium chloride 45                                                         sodium chloride    27                                                         cryolite (3NaF.AlF.sub.3)                                                                        22                                                         lithium chloride    6                                                         ______________________________________                                    

Said flux makes it possible to carry out a stable process of electroslagwelding, reduces well the oxide film on the welded parts. However, theweld obtained with the use of said flux in the process of welding, isporous and contains an increased amount of gases, thereby resulting inthe sharp decrease in mechanical characteristics of welded joints.

DISCLOSURE OF INVENTION

The object of the invention is the provision of a method of electroslagwelding of light metals, a forming device and a flux, permitting, bychanging process parameters, structural arrangement and by qualitativevariation of the flux, the provision of monitoring the composition andstructure of the weld metal, thereby upgrading performancecharacteristics of the weld.

The object set forth is attained by the fact that in a method ofelectroslag welding light metals, comprising successively mounting partsto be welded, providing a desired gap therebetween, a forming device andan electrode, filling the gap with a flux and setting up a slag poolfollowed by melting the electrode and the edges to be welded with theformation of a metal pool which is accumulated, maintained in the liquidstate and utilized to fill the weld gap with the liquid metal withsubsequent solidification of the liquid metal, according to theinvention, the metal pool is accumulated outside the gap above the edgesto be welded, and filling the gap with the liquid metal is accomplishedafter the fusion of the electrode and the edges of the parts andaccumulation of the pool in the amount required for filling the gapconsidering weld reinforcement.

The method allows the performance characteristics to be improved due toa practically complete degassing and refining of the weld metal duringthe accumulation of the metal pool outside the gap above the edges to bewelded.

The metal pool is recommended to be additionally blown with an inertgas.

The above modification of the method allows the process of degassing tobe intensified.

It is expedient that the inert gas is argon. Said modification of themethod is the most economical.

It is possible to introduce additionally into the metal pool substancesforming complex compounds with harmful impurities, said compounds beinginsoluble in metal.

The above modification of the method allows liquid metal to be purifiedfrom harmful impurities prior to filling the gap.

It is recommended to use calcium in an amount of 0.15 to 0.5 percent byweight as the substance forming a complex compound with harmfulimpurities, said compound being insoluble in metal.

The above modification of the method makes it possible to withdrawharmful impurities of iron from liquid metal.

It is expedient to use magnesium in an amount of 0.1 to 1.5 percent byweight as the substance forming a complex compound with harmfulimpurities, said compound being insoluble in metal.

Said modification of the method permits harmful impurities of silicon tobe removed from liquid metal.

The object set forth is also attained by the fact that in a formingdevice comprising moulds, a container disposed above the edges to bewelded, a container disposed under the edges to be welded, according tothe invention, the moulds are further provided with porous elements andare constructed with stepped (i.e., rectangular in shape and parallel toone another) longitudinal grooves forming a supporting platform on whichare disposed said porous elements forming, together with said grooves,enclosed cavities, the container disposed above the edges to be weldedbeing further provided with internal and external terminals and a jumperconnecting the internal terminals, and the container disposed under theedges to be welded is further provided with a transverse partition.

The device ensures the possibility of carrying out the welding processwith practically complete degassing and refining of the weld metal. Thedevice also permits the simplification of setting up the slag pool.

The metallic jumper is recommended to be constructed from a metal havinga low melting point.

The above modification provides for self-adjustment of the process ofsetting up the slag pool.

Said modification ensures obtaining a weld whose composition isidentical to that of the welded parts.

It is possible that the metallic jumper be constructed from a metalidentical to the metal to be welded, said metal containing alloyingcomponents.

The above modification ensures additional alloying of the weld metal.

It is recommended to determine the content of each alloying componentfrom the following formula: ##EQU1## where L_(j) is a content of thealloying component in the jumper, %;

L_(w) is a content of the alloying component in the weld, %;

L_(wm) is a content of the alloying component in the welded material, %;

L_(e) is a content of the alloying component in the electrode, %;

V_(w) is a volume of the weld, cm³ ;

V_(j) is a volume of the jumper, cm³ ;

γ is a portion of the welded metal in the weld metal.

The jumper is expedient to be constructed from a refractory materialhaving high electrical resistivity.

The above modification ensures intensification of the process of settingup the slag pool and accompanying heating of the metal pool.

It is most economical to utilize graphite as the refractory materialhaving high electrical resistivity.

It is recommended to construct the partition from a material having alow melting point.

This modification simplifies the final stage of the process.

A metal identical to the welded one is possible to be utilized as thematerial having a low melting point.

The above modification provides for the possibility of obtaining a weldhaving minimum content of impurities.

It is recommended to construct the partition from a material reactingwith the slag.

Said modification allows the final stage of the process to beintensified.

It is economical to utilize dinas as the material reacting with theslag.

The partition is expedient to be constructed from a refractory materialand provided with a slot for mounting the electrode.

The above modification predetermines repeated utilization of thepartition.

It is economical to utilize graphite as the refractory material.

The object set forth is also attained by the fact that a flux based onhalides, according to the invention, contains cryolite, barium fluoride,and alkali metal bromide.

The flux enables the process stability to be improved, thereby upgradingperformance characteristics of the welded joints.

It is expedient that the flux contain components taken in the followingratio, percent by weight;

    ______________________________________                                        barium fluoride  65.0-75.0                                                    cryolite         15.0-25.0                                                    alkali metal bromide                                                                            5.0-10.0                                                    ______________________________________                                    

Said composition of the flux makes it possible to upgrade the chemicalactivity with oxide films existing on the edges being welded.

It is most expedient to utilize sodium bromide as the alkali metalbromide.

Said modification allows the process of destructing an oxide film to beintensified.

BRIEF DESCRIPTION OF DRAWINGS

The invention is further explained in terms of detailed description ofthe best embodiment thereof with reference to the accompanying drawings,in which:

FIG. 1 shows schematically the initial stage of the welding process ofthe invention;

FIG. 2 shows schematically the intermediate stage of the welding processof the invention;

FIG. 3 shows schematically the final stage of the welding process of theinvention;

FIG. 4 shows schematically the forming device of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Welding of aluminium specimens was carried out. For this purposespecimens 1 were mounted on supports with a gap 2 therebetween.Following this, a forming device was assembled on the parts to bewelded, and an electrode 3 was mounted. The electrode 3 is disposedalong the axis of the gap 2 between the edges to be welded of thespecimens 1. Next, the gap 2 is filled with a flux 4. The forming deviceand the electrode 3 are connected to different poles of a power source,and a slag pool 5 is set up. After setting up the slag pool 5, thewelding current was switched on, thereby resulting in the initiation ofthe welding process (FIGS. 1-3).

The welding electrode 3 and the edges of the specimens 1 are melted,drops of melted metal 6 float to the surface of a more dense slag,thereby forming on the surface thereof a metal pool 7, which pool ismaintained in the liquid state outside the gap 2 above the parts beingwelded. The metal pool 7 may be blown with argon or helium. A mixture ofargon and helium may be also utilized. After the accumulation of themetal pool 7 in an amount required for filling the gap 2 consideringweld reinforcement, the slag pool 5 is moved out of the gap 2. The placethus liberated in the gap 2 is filled with the liquid metal of the metalpool 7, which metal forms a weld 8 after solidification.

A forming device providing for the above described welding process,comprises moulds 9 having stepped longitudinal grooves 10 forming asupporting platform 11. On the supporting platform 11 are mounted porouselements 12 constructed, e.g., from activated carbon. In the fixation ofthe porous elements 12 on the supporting platforms 11 enclosedlongitudinal cavities are formed within side surfaces of the moulds 9,said cavities allowing gases to be discharged out of the gap in theprocess of welding. The height of the moulds 9 is determined by theheight of the parts 1 and does not depend on the thickness. The formingdevice further comprises a container 13 disposed above the edges to bewelded (an accumulation chamber) and a container 14 located under saidedges (a receiver). The walls of the accumulation chamber 13 are formedby the moulds 9 and bars 15 made from graphite, said bars being mountedon the parts 1. The bars 15 are provided with terminals 16, 17. Theinternal terminals 17 are connected with each other by a jumper 18. Thejumper 18 may be constructed from a material having a low melting pointwhich material may be a metal identical to that being welded (FIG. 4).

The metal identical to that being welded may further contain alloyingcomponents. The content of each alloying component is calculated fromthe following formula: ##EQU2## where L_(j) is a content of the alloyingcomponent in the jumper, %;

L_(w) is a content of the alloying component in the weld, %;

L_(wm) is a content of the alloying component in the welded material, %;

L_(e) is a content of the alloying component in the electrode, %;

V_(w) is a volume of the weld, cm³ ;

V_(j) is a volume of the jumper, cm³ ;

γ is a portion of the welded metal in the weld metal.

It is necessary to consider in the calculations the losses of alloyingcomponents in the welding process.

The jumper 18 may be also constructed from a refractory material havinghigh electrical resistivity, e.g. tungsten or graphite.

The accumulation chamber 13 is provided with a cover 19 in which thereis provided an opening 20 for supplying the flux and gas for creating aprotective atmosphere over the surface of the metal pool 7. For feedingthe flux 4 the cover 19 may comprise a feed hopper 21. The feed hopper21 has an outlet duct 22 which may be provided with an electromagneticshutter 23. The coil of the shutter is connected to a power source (notshown) by a switch 24.

The walls of the container 14 located under the parts to be welded areformed by the moulds 9 and run-off plates 25 constructed from graphite.A tray 26 of said container is made from graphite. The receivercomprises a transverse partition 27 dividing its cavity into twoportions.

The partition 27 may be constructed from a material having a low meltingpoint, e.g. from a metal identical to that being welded. Such materialsas dinas or fireclay, which react with the slag, may be utilized.

The partition 27 may be also constructed from a refractory material,e.g. graphite. In this case the partition 27 is provided with a slot formounting the electrode 3.

To practice the method of the invention, a halide-based flux isutilized, said flux containing cryolite, barium fluoride, and alkalimetal bromide taken in the following ratio, percent by weight:

    ______________________________________                                        barium fluoride  65.0-75.0                                                    cryolite         15.0-25.0                                                    alkali metal bromide                                                                            5.0-10.0                                                    ______________________________________                                    

Conventional alkali metal bromides may be utilized as the alkali metalbromide, although the most effective is sodium bromide.

The forming device operates as follows. After this device has beenassembled on the parts 1 to be welded, said parts made, e.g. fromaluminium, the plate electrode 3 is introduced through the slot providedin the partition 27 and into the gap 2 between the specimens 1 to bewelded. On the internal terminals 17 of the bars 15 of the accumulationchamber 13 is fixed the jumper 18 made from a refractory material, e.g.graphite. The welding gap 2 and the cavity of the accumulation chamber13 are filled with the solid flux 4 via the feed hopper 21. The flux 4fills the accumulation chamber 13 so that the jumper 18 is surroundedfrom all the sides by the flux 4.

The contacts of the switch 24 of the shutter 23 are closed, i.e. theelectromagnetic coil of the shutter 23 is connected to a power supply(not shown), thereby resulting in closing the outlet duct 22 of the feedhopper 21.

A welding current power supply (not shown) is connected to the externalterminals 16 of the bars 15. The current, while passing along thegraphite jumper 18, overheats the latter, which in turn causes meltingof the flux 4 within the cavity of the accumulation chamber 13, i.e. theslag pool is formed. Liquid metal of the melted electrode, floating inthe more dense slag pool, forms the metal pool 7.

As the jumper 18 is made from a material having a low melting point,being aluminium in the given case, the metal of the melted jumper mixeswith the metal pool 7.

At the moment when the jumper gets melted, which is determined fromchanges in the readings of an ammeter and voltmeter, the thermal circuitis disconnected and the welding circuit is connected.

A protective medium is created over the surface of the metal pool. Thisis accomplished by supplying an inert gas into the accumulation chamberthrough the opening 20 provided in the cover 19 or through the feedhopper 21.

After the electrode 3 has been fused below the level of the partition27, the slag pool moves into the receiver 14, and the metal pool 7 movesinto the gap between the parts 1 being welded.

In the case of utilization of the partition 27 made from a materialidentical to that being welded, after complete melting of the fluxwithin the gap, said partition gets melted under the effect of the heatof the slag pool, the metal of the partition mixes with the metal pool 7within the gap 2, and the slag pool 5 moves into the receiver 14. In theutilization of the partition 27 constructed from a material reactingwith the slag after the complete melting of the flux within the gap, thematerial of said partition 27 reacts with the liquid slag 5 therebyresulting in the destruction of the partition 27. The material of thepartition 27 passes into the slag pool 5. Similar to the above describedmodifications of the operation of the device, the slag pool 5 is thenreplaced within the gap by the liquid metal from the metal pool 7.

The invention is further explained in terms of specific examples.

EXAMPLE 1

Aluminium specimens having a cross-section of 100×100 mm were welded.The parts to be welded were mounted with a gap of 65 mm. Following this,a forming device and an electrode were mounted.

The jumper of the accumulation chamber of the forming device was madefrom aluminium.

The partition of the receiver of the forming device was made fromgraphite and provided with an opening to receive the electrode.

A flux of the following composition, in percent by weight, was fed intothe gap between the edges to be welded:

    ______________________________________                                               barium fluoride                                                                         65.0                                                                cryolite  25.0                                                                sodium bromide                                                                          10.0                                                         ______________________________________                                    

After a slag pool had been set up, melting of the electrode and fusionof the edges occured with the formation of the metal pool.

    ______________________________________                                        Welding was performed at the following conditions:                            welding current = 6.0 kA                                                      no-load voltage = 34.0 V                                                      welding voltage = 30.0 V                                                      ______________________________________                                    

The metal pool was accumalated above the edges within the accumulationchamber and was maintained in the liquid state. After said pool had beenaccumulated in a volume of 700 to 750 cm³, the slag pool was moved fromthe gap into the receiver and was replaced by liquid metal, which formedthe weld in the process of solidification. The welding time was 12 min.

EXAMPLE 2

Aluminium specimens having a cross-section of 100×100 mm were welded.The parts to be welded were mounted with a gap of 60 mm. Following this,a forming device and an electrode were mounted.

The jumper of the accumulation chamber of the forming device was madefrom aluminium alloyed with magnesium.

The partition of the receiver of the forming device was made from dinas.

A flux of the following composition, in percent by weight, was fed intothe gap between the edges:

    ______________________________________                                               barium fluoride                                                                         75.0                                                                cryolite  20.0                                                                sodium bromide                                                                          5.0                                                          ______________________________________                                    

After a slag pool had been set up, melting of the electrode and theedges to be welded occured with the formation of a slag and metal pool.The metal pool was accumulated above the edges being welded and wasmaintained in the liquid state. The metal pool was also blown throughwith argon.

After the metal pool had been accumulated and all the flux disposedwithin the gap had been melted, the material of the partition of thereceiver reacted with the slag. As a result of this reaction, thepartition was destructed, the slag moved into the receiver, and themetal of the metal pool moved into the gap.

Welding was performed at the following conditions:

welding current=5.0 kA

welding voltage=27.0 V

As a result of the welding, a weld was formed containing 6.5% Mg.

EXAMPLE 3

Magnesium specimens having a cross-section of 80×90 mm were welded. Theparts to be welded were mounted with a gap of 55 mm. Following this, aforming device and a magnesium electrode were mounted.

The jumper of the accumulation chamber was made from graphite.

The partition of the receiver of the forming device was made frommagnesium.

A flux of the following composition, in percent by weight, was fed intothe gap between the edges to be welded:

    ______________________________________                                               barium fluoride                                                                         70.0                                                                cryolite  22.0                                                                sodium bromide                                                                          8.0                                                          ______________________________________                                    

After a slag pool had been set up, melting of the electrode and fusionof the edges occured with the formation of a metal pool.

    ______________________________________                                        Welding was performed at the following conditions:                            welding current = 6,5 kA                                                      welding voltage = 28.0 V                                                      ______________________________________                                    

As a result of the welding, a weld was obtained. The welding time was 14min.

Mechanical tests demonstrated that the ultimate strength of the weldmetal obtained in accordance with Examples 1 through 3 was not less than0.85 of the ultimate strength of the base metal.

While particular embodiments of the invention have been shown anddescribed, various modifications thereof will be apparent to thoseskilled in the art and therefore it is not intended that the inventionbe limited to the disclosed embodiments or to the details thereof andthe departures may be made therefrom within the spirit and scope of theinvention as defined in the claims.

INDUSTRIAL APPLICABILITY

The method of electroslag welding of light metals, the forming device,and the flux are used for welding light metals having a density which islower than that of the slag.

We claim:
 1. A method of electroslag welding of light metals to producea desire weld reinforcement in which parts having edges to be welded, aforming device, and an electrode are successively mounted and a requiredwelding gap between said parts provided, following which the gap isfilled with a flux, a slag pool is set up and a metal pool is formed bymelting the electrode and the edges of said parts, said pool isaccumulated, maintained in the liquid state and utilized for filling thewelding gap with the liquid metal with subsequent solidification of theliquid metal, said method comprising: accumulating the metal pooloutside the gap above the parts being welded; and filling the gap withthe liquid metal after fusion of the electrode and the edges of theparts has been completed and the accumulated metal pool has a volumesufficient to fill the gap in view of the desired weld reinforcement. 2.A method as defined in claim 1, wherein the metal pool is additionallyblown with an inert gas.
 3. A method as defined in claim 2, wherein theinert gas is argon.
 4. A method as defined in claim 1, whereinsubstances forming complex compounds with harmful impurities and beinginsoluble in the metal are additionally introduced into the metal pool.5. A method as defined in claim 4, wherein the substance forming acomplex compound with harmful impurities and being insoluble in themetal is calcium taken in an amount of 0.15 to 0.5 percent by weight. 6.A method as defined in claim 4, wherein the substance forming a complexcompound with harmful impurities and being insoluble in the metal ismagnesium taken in an amount of 0.1 to 1.5 percent by weight.
 7. Aforming device for electroslag welding of light metals, comprisingmoulds, a container disposed above parts to be welded, and a containerdisposed under the parts to be welded, wherein the moulds are furtherprovided with porous elements and constructed with longitudinal grooveswhich are rectangular in shape and parallel to one another and whichform a supporting platform on which are disposed said porous elementsforming together with the grooves enclosed cavities, the containerdisposed above the parts being further provided with external andinternal terminals, a jumper connecting the internal terminals and thecontainer disposed under the parts is further provided with a transversepartition.
 8. A forming device as defined in claim 7, wherein the jumperis made from a material having a low melting point.
 9. A forming deviceas defined in claim 8, wherein the material having a low melting pointin a metal identical to that being welded.
 10. A forming device asdefined in claim 7, wherein the jumper is made of a metal identical tothat being welded, said metal containing alloying components.
 11. Aforming device as defined in claim 10, wherein the content of eachalloying component in the metallic jumper is calculated from theformula: ##EQU3## where L_(j) is a content of the alloying component inthe jumper, %;L_(w) is a content of the alloying component in the weld,%; L_(wm) is a content of the alloying component in the welded material,%; L_(e) is a content of the alloying component in the electrode, %;V_(w) is a volume of the weld, cm³ ; V_(j) is a volume of the jumper,cm³ ; γ is a portion of the welded metal in the weld metal.
 12. Aforming device as defined in claim 7, wherein the jumper is made from arefractory material having high electrical resistivity.
 13. A formingdevice as defined in claim 12, wherein the refractory material havinghigh electrical resistivity is graphite.
 14. A forming device as definedin claim 7, wherein the partition is made from a material having a lowmelting point.
 15. A forming device as defined in claim 14, wherein thematerial having a low melting point is a metal identical to that beingwelded.
 16. A forming device as defined in claim 7, wherein thepartition is made from a material reacting with the slag.
 17. A formingdevice as defined in claim 16, wherein the material reacting with theslag is dinas.
 18. A forming device as defined in claim 7, wherein thepartition is made from a refractory material and is provided with a slotfor mounting the electrode.
 19. A forming device as defined in claim 18,wherein the refractory material is graphite.
 20. A flux for electroslagwelding of light metals, based on halides, wherein said flux containscryolite, barium fluoride, and alkali metal bromide.
 21. A flux asdefined in claim 20, wherein said flux contains components in thefollowing ratio, percent by weight:

    ______________________________________                                        barium fluoride  65.0-75.0                                                    cryolite         15.0-25.0                                                    alkali metal bromide                                                                            5.0-10.0                                                    ______________________________________                                    


22. A flux as defined in claim 20, wherein the alkali metal bromide issodium bromide.